The sense of taste is active in food recognition, in motivating ingestion and triggering certain reflexive digestive processes. In spite of recent advances, however, our knowledge of the peripheral biochemical mechanisms in taste is inadequate. While a receptor hypothesis is attractive, receptor macromolecules unique to taste receptor cells have not been demonstrated. Also, the biochemical mechanisms operative during transduction of the chemical message through the taste cells to the innervating nerve are not understood. This proposal plans to use fluorescent probe techniques in an attempt to gain information about these events. We will use a system which permits the observation of either intrinsic or extrinsic fluorescence from taste buds in situ. Recent work has suggested that ions imparting a salty taste change the levels of reduced pyridine nucleotide in the circumvallate papillae from bovine tongue. We will explore further the nature and specificity of this change. Fluorescence from extrinsic sources, either as dyes or as stimuli, can also be used in this intact system to observe the interaction of stimulus with receptor or, in the case of nonstimulating and passive dyes, to monitor the transductive event. Experiments using bitter stimuli will attempt to explore further the binding specificity for this modality. Collaborative efforts are planned with morphologists and neurophysiologists. Our ultimate aim is to find fluorescent agents which can passively label taste cells in situ and report their activity toward stimulating chemicals.